μ-Law-to-a-law translating equipment and a-law-to-μ-law translating equipment

ABSTRACT

μ-law-to-A-law translating equipment is used for plural PCM telephone lines installed between countries different in a conversion law. This translating equipment is provided with plural μ-law signal receiving circuits, a multiplexer, a μ-law-to-A-law converter, a demultiplexer, plural A-law signal output circuits and a timing pulse generator. Each μ-law signal receiving circuit outputs parallel μ-law PCM signals synchronized with a reference frame pulse and the multiplexer time-division multiplexes these signals according to a time division system. The μ-law-to-A-law converter outputs a time-division multiplexed A-law PCM signal, the demultiplexer demultiplexes this time-division multiplexed signal and outputs plural parallel A-law PCM signals. The A-law signal output circuit outputs a serial A-law PCM signal to which a frame bit is added.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to μ-law and A-law which are respectively an international standard for PCM digital transmission of telephonic speech, particularly relates to μ-law-to-A-law translating equipment and A-law-to-μ-law translating equipment.

2. Description of the Related Prior Art

For a PCM telephone line, there are a line encoded according to μ-law and a line encoded according to A-law based upon ITU-T Rec. G. 711. μ-law is used in Japan and North America and A-law is used in European countries. Therefore, in case an international PCM telephone line is laid between two countries different in a conversion law, a PCM speech signal is required to be converted to a different conversion law in a connection between communication networks of both countries. For this conversion, a μ-law-to-A-law converter and an A-law-to-μ-law converter are used. For example, a μ-law-to-A-law converter or an A-law-to-μ-law converter is provided every line to a primary PCM telephone line of 1.544 Mbits/s or 2.048 Mbits/s. In case the number of lines is increased, these converters are required to be also increased by the same number as the number of lines. However, when the μ-law-to-A-law converter or the A-law-to-μ-law converter is increased, the cost is increased and the reliability is deteriorated.

SUMMARY OF THE INVENTION

Therefore, the object of the invention is to provide a μ-law-to-A-law converter and an A-law-to-μ-law converter respectively not required to be increased even if PCM telephone lines between two countries different in a conversion law are increased.

To achieve the object of the invention, μ-law-to-A-law translating equipment is provided with a timing pulse generator that generates a reference frame pulse, a μ-law signal receiving circuit that receives a μ-law PCM signal and outputs parallel μ-law PCM signals according to a reference frame pulse, a multiplexer that time-division multiplexes plural parallel μ-law PCM signals and outputs a time-division multiplexed μ-law PCM signal, a μ-law-to-A-law converter that converts the time-division multiplexed μ-law PCM signal to a time-division multiplexed A-law PCM signal, a demultiplexer that demultiplexes the time-division multiplexed A-law PCM signal and outputs plural parallel A-law PCM signals and an A-law signal output circuit that receives the parallel A-law PCM signals and outputs a serial A-law PCM signal.

Also, A-law-to-μ-law translating equipment is provided with a timing pulse generator that generates a reference frame pulse, an A-law signal receiving circuit that receives an A-law PCM signal and outputs parallel A-law PCM signals according to a reference frame pulse, a multiplexer that time-division multiplexes plural parallel A-law PCM signals and outputs a time-division multiplexed A-law PCM signal, an A-law-to-μ-law converter that converts the time-division multiplexed A-law PCM signal to a time-division multiplexed μ-law PCM signal, a demultiplexer that demultiplexes the time-division multiplexed μ-law PCM signal and outputs plural parallel μ-law PCM signals and a μ-law signal output circuit that receives the parallel μ-law PCM signals and outputs a serial μ-law PCM signal.

In an embodiment of the invention, the μ-law signal receiving circuit is provided with a line receiver that converts a μ-law PCM signal from bipolar to unipolar and outputs a unipolar μ-law signal, a frame buffer that temporarily stores the unipolar μ-law signal, a frame detector that detects the frame leading part of the unipolar μ-law signal and generates an address reset pulse synchronized with the frame leading position for writing to the frame buffer, a frame position comparator that measures the time lag in a position of a reference frame pulse and the address reset pulse for writing to the frame buffer and generates an address reset pulse for reading from the frame buffer and a serial-parallel converter that converts a serial μ-law PCM signal read from the frame buffer to parallel μ-law PCM signals. Also, the A-law signal receiving circuit is provided with a line receiver that converts an A-law PCM signal from bipolar to unipolar and outputs a unipolar A-law signal, a frame buffer that temporarily stores the unipolar A-law signal, a frame detector that detects the frame leading part of the unipolar A-law signal and generates an address reset pulse synchronized with the frame leading position for writing to the frame buffer, a frame position comparator that measures the time lag in a position of a reference frame pulse and the address reset pulse for writing to the frame buffer and generates an address reset pulse for reading from the frame buffer and a serial-parallel converter that converts a serial A-law PCM signal read from the frame buffer to parallel A-law PCM signals. The μ-law-to-A-law converter and the A-law-to-μ-law converter can correspond by adding a receiving circuit and a transmitting circuit even if telephone lines are increased.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become apparent from the following detailed description when taken with the accompanying drawings in which:

FIG. 1 is a block diagram showing μ-law-to-A-law translating equipment that contains two lines;

FIG. 2 is a timing chart showing each signal of the μ-law-to-A-law translating equipment that contains two lines;

FIG. 3 is a block diagram showing μ-law-to-A-law translating equipment that contains three or more lines;

FIG. 4 is a block diagram showing A-law-to-μ-law translating equipment that contains two lines;

FIG. 5 is a block diagram showing A-law-to-μ-law translating equipment that contains three or more lines; and

FIG. 6 is a block diagram showing μ-law-to-A-law translating equipment and A-law-to-μ-law translating equipment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows μ-law-to-A-law translating equipment that contains two lines equivalent to a first embodiment of the invention. The μ-law-to-A-law translating equipment is provided with a multiplexer 7 before a μ-law-to-A-law converter 8 and a demultiplexer 9 after it. The μ-law-to-A-law translating equipment is also provided with two μ-law signal receiving circuits 1 a and 1 b before the multiplexer 7 and is provided with two A-law signal output circuits 13 a and 13 b after the demultiplexer 9. The μ-law signal receiving circuits 1 a and 1 b have the same configuration and the A-law signal output circuits 13 a and 13 b also have the same configuration. The μ-law-to-A-law translating equipment contains two primary PCM telephone lines, however, only one μ-law-to-A-law converter 8 is mounted in the equipment. The equipment is also provided with a timing pulse generator 35 that outputs a reference frame pulse 32 to the μ-law signal receiving circuits 1 a and 1 b and the A-law signal output circuits 13 a and 13 b. The μ-law signal receiving circuit 1 a is provided with a line receiver 2 a, a frame buffer 4 a, a frame detector 3 a, a frame position comparator 5 a and a serial-parallel converter 6 a. The line receiver 2 a converts a μ-law primary PCM signal 21 a input to the μ-law-to-A-law translating equipment from bipolar to unipolar and outputs a unipolar μ-law primary signal 22 a. The frame buffer 4 a is a memory for temporarily storing a unipolar μ-law primary signal 22 a output from the line receiver 2 a and is a first-in first-out (FIFO) memory having data capacity for two frames for example. The frame detector 3 a detects the frame leading part of a unipolar μ-law primary signal 22 a and outputs an address reset pulse 24 a synchronized with the frame leading position for writing to the frame buffer to the frame buffer 4 a and the frame position comparator 5 a. The frame position comparator 5 a compares the position of a reference frame pulse 32 output from the timing pulse generator 35 and an address reset pulse 24 a for writing to the frame buffer and counts the time lag in a position of these pulses according to a clock signal inside the μ-law-to-A-law translating equipment not shown. This comparator 5 a outputs an address reset pulse 25 a for reading from the frame buffer to the frame buffer 4 a based upon the result of the count. The serial-parallel converter 6 a converts a serial μ-law PCM signal 27 a in units of 8 bits read from the frame buffer 4 a to 8-bit parallel signals and outputs parallel μ-law PCM signals 23 a. The μ-law signal receiving circuit 1 b is also provided with the same configuration and function as those of the μ-law signal receiving circuit 1 a. The multiplexer 7 time-division multiplexes parallel μ-law PCM signals 23 a and 23 b respectively output from the serial-parallel converters 6 a and 6 b and outputs a time-division multiplexed μ-law PCM signal 28. The well-known μ-law-to-A-law converter 8 converts the time-division multiplexed μ-law PCM signal 28 to a time-division multiplexed A-law PCM signal 29. The demultiplexer 9 demultiplexes the time-division multiplexed A-law PCM signal 29 and outputs parallel A-law PCM signals 31 a and 31 b to the A-law signal output circuits 13 a and 13 b. The A-law signal output circuit 13 a is provided with a parallel-serial converter 10 a and a frame inserter 11 a and further, can be also provided with a line driver 12 a. The parallel-serial converter 10 a converts the parallel A-law PCM signals 31 a to a serial signal and outputs a serial A-law PCM signal 30 a. The frame inserter 11 a inserts frame bits required for the serial A-law PCM signal 30 a based upon a reference frame pulse 32 output from the timing pulse generator 35. The line driver 12 a adjusts a serial A-law PCM signal 33 a so that it is at a predetermined output amplitude level and outputs an A-law primary PCM signal 34 a. The A-law signal output circuit 13 b is also provided with the same configuration and function as those of the A-law signal output circuit 13 a.

Referring to FIG. 2, the operation of the μ-law-to-A-law translating equipment will be described below. The corresponding numbers in the two μ-law signal receiving circuits 1 a and 1 b will be both described below. The line receivers 2 a and 2 b respectively convert μ-law primary PCM signals 21 a and 21 b and respectively output unipolar μ-law primary signals 22 a and 22 b ((1) and (3) in FIG. 2). The frame detectors 3 a and 3 b detect the respective frame position of the μ-law primary PCM signals 21 a and 21 b. The frame detectors 3 a and 3 b also respectively generate address reset pulses 24 a and 24 b ((2) and (4) in FIG. 2) synchronized with the detected frame for writing to the frame buffer. These address reset pulses 24 a and 24 b are respectively output to the frame buffers 4 a and 4 b and the frame position comparators 5 a and 5 b. The frame position comparators 5 a and 5 b receive a reference frame pulse 32 ((5) in FIG. 2) which the timing pulse generator 35 outputs and measure time lag between the pulse 32 and the address reset pulses for writing to the frame buffer 24 a and 24 b. The frame position comparators 5 a and 5 b respectively output address reset pulses synchronized with a reference frame pulse 32 for reading from the frame buffer 25 a and 25 b to the frame buffers 4 a and 4 b so as to read a PCM signal stored in the frame buffers 4 a and 4 b. As a result, serial μ-law PCM signals 27 a and 27 b ((6) and (7) in FIG. 2) synchronized with a reference frame pulse 32 are respectively read from the frame buffers 4 a and 4 b. When a reference frame pulse 32 and an address reset pulse for writing to the frame buffer 24 a are close or occur at the same timing, reading operation and writing operation from/to the same data area simultaneously occur in the frame buffer 4 a and the normal reading and writing of data are disabled. In such a case, the frame position comparator 5 a advances or slows an address reset pulse for reading from the frame buffer 25 a by one frame to prevent simultaneous occurrence of both operation. Further, the serial-parallel converters 6 a and 6 b respectively convert serial μ-law PCM signals 27 a and 27 b which are a serial signal in units of 8 bits to parallel μ-law PCM signals 23 a and 23 b ((8) and (9) in FIG. 2). As a result, even if μ-law primary PCM signals 21 a and 21 b are not synchronous, parallel μ-law PCM signals 23 a and 23 b ((8) and (9) in FIG. 2) are synchronous with a reference frame pulse 32 ((5) in FIG. 2). The multiplexer 7 time-division multiplexes the parallel μ-law PCM signals 23 a and 23 b ((8) and (9) in FIG. 2) and outputs as a time-division multiplexed μ-law PCM signal 28 ((10) in FIG. 2).

The μ-law-to-A-law converter 8 successively converts the time-division multiplexed μ-law PCM signal 28 to the corresponding A-law bit pattern and outputs a time-division multiplexed A-law PCM signal 29. The demultiplexer 9 demultiplexes the signal 29 and outputs parallel A-law PCM signals 31 a and 31 b. The parallel-serial converters 10 a and 10 b respectively convert the parallel A-law PCM signals 31 a and 31 b to serial A-law PCM signals 30 a and 30 b. The frame inserters 11 a and 11 b respectively insert a frame bit according to the frame format of a primary line according to A-law into the serial A-law PCM signals 30 a and 30 b according to a reference frame pulse received from the timing pulse generator 35. The line drivers 12 a and 12 b respectively convert serial A-law PCM signals 33 a and 33 b to which the frame bit is added from unipolar to bipolar and respectively output A-law primary PCM signals 34 a and 34 b at a predetermined output level.

FIG. 3 shows an example of μ-law-to-A-law translating equipment that contains three or more lines. This equipment is provided with three or more μ-law signal receiving circuits 1 a to lx, a multiplexer 7, a μ-law-to-A-law converter 8, a demultiplexer 9, A-law signal output circuits 13 a to 13 x of the same number as that of the μ-law signal receiving circuits and a timing pulse generator 35. Each μ-law signal receiving circuit 1 a to 1 x has the same configuration and each A-law signal output circuit 13 a to 13 x also has the same configuration. The multiplexer 7 time-division multiplexes parallel μ-law PCM signals 23 a to 23 x output by each μ-law signal receiving circuit 1 a to 1× and outputs a time-division multiplexed μ-law PCM signal 28. The μ-law-to-A-law converter 8 converts the μ-law PCM signal 28 to an A-law bit pattern and outputs a time-division multiplexed A-law PCM signal 29. The demultiplexer 9 demultiplexes the signal 29 and outputs parallel A-law PCM signals 31 a to 31× to the A-law signal output circuits 13 a to 13 x. The A-law signal output circuits 13 a to 13 x respectively output A-law primary PCM signals 34 a to 34 x.

FIG. 4 shows an example of A-law-to-μ-law translating equipment that contains two lines. This A-law-to-μ-law translating equipment is provided with A-law signal receiving circuits 401 a and 401 b, a multiplexer 407, an A-law-to-μ-law converter 408, a demultiplexer 409, μ-law signal output circuits 413 a and 413 b and a timing pulse generator 35. The A-law-to-μ-law translating equipment is similar to the μ-law-to-A-law translating equipment in configuration and a function, however, they are different in a signal processed by them. A-law primary PCM signals 421 a and 421 b are respectively input to the A-law signal receiving circuits 401 a and 401 b, are respectively converted to parallel A-law PCM signals 423 a and 423 b respectively synchronized with a reference frame pulse 32 and are output to the multiplexer 407. The multiplexer 407 time-division multiplexes the parallel A-law PCM signals 423 a and 423 b. The A-law-to-μ-law converter 408 converts the signals 423 a and 423 b to a time-division multiplexed μ-law PCM signal 429. The demultiplexer 409 demultiplexes the signal 429 and respectively outputs parallel μ-law PCM signals 431 a and 431 b to the μ-law signal output circuits 413 a and 413 b. In the μ-law signal output circuits 413 a and 413 b, the signals 431 a and 431 b are converted to serial μ-law PCM signals 430 a and 430 b, a frame bit according to the frame format of the primary line according to μ-law is inserted by the frame inserters 411 a and 411 b and the signals are output as μ-law primary PCM signals 434 a and 434 b at a predetermined output level.

FIG. 5 shows an example of A-law-to-μ-law translating equipment that contains three or more lines. This equipment is provided with three or more A-law signal receiving circuits 401 a to 401 x, a multiplexer 407, a A-law-to-μ-law converter 408, a demultiplexer 409, μ-law signal output circuits 413 a to 413 x of the same number as that of the A-law signal receiving circuits and a timing pulse generator 35. Each A-law signal receiving circuit has the same configuration as the above-mentioned μ-law signal receiving circuit though processed signals are different. Each μ-law signal output circuit is also similar. The multiplexer 407 time-division multiplexes parallel μ-law PCM signals 423 a to 423 x output by each A-law signal receiving circuit 401 a to 401× and outputs a time-division multiplexed A-law PCM signal 428. The A-law-to-μ-law converter 408 converts the A-law PCM signal 428 to a μ-law bit pattern and outputs a time-division multiplexed μ-law PCM signal 429. The demultiplexer 409 demultiplexes the signal 429 and outputs parallel I-law PCM signals 431 a to 431 x to the μ-law signal output circuits 413 a to 413 x. The μ-law signal output circuits 413 a to 413 x respectively output μ-law primary PCM signals 434 a to 434 x.

FIG. 6 shows an example of μ-law-to-A-law and A-law-to-μ-law translating equipment. This equipment is provided with the μ-law-to-A-law translating equipment that contains three or more lines shown in FIG. 3 and the A-law-to-μ-law translating equipment that contains three or more lines shown in FIG. 5. This equipment can execute the mutual conversion of μ-law and A-law. The equipment shown in FIG. 6 receives μ-law primary PCM signals 21 a to 21 x, outputs A-law primary PCM signals 34 a to 34 x, similarly receives A-law primary PCM signals 421 a to 421× and outputs μ-law primary PCM signals 434 a to 434 x.

The translating equipment according to the invention locks the phase of input plural signals in units of octet composed of 8 bits inside the equipment and converts to 8-bit parallel data. As a result, the equipment can time-division multiplex input data from two lines and can execute μ-law-to-A-law conversion (or A-law-to-μ-law conversion) using only one μ-law-to-A-law converter (or only one A-law-to-μ-law converter) for the parallel input-output of 8 bits. Therefore, this equipment can have simple circuit configuration and the reliability is enhanced at a low cost.

While the present invention has been described in connection with certain preferred embodiments, it is to be understood that the subject matter encompassed by the present invention is not limited to those specific embodiments. On the contrary, it is intended to include all alternatives, modifications, and equivalents as can be included within the spirit and scope of the following claims. 

1. μ-law-to-A-law translating equipment, comprising: a timing pulse generator that generates a reference frame pulse; a μ-law signal receiving circuit that receives a μ-law PCM signal and outputs parallel μ-law PCM signals according to a reference frame pulse, said μ-law signal receiving circuit comprising: a line receiver that converts the μ-law PCM signal from bipolar to unipolar and outputs a unipolar μ-law signal, a frame buffer that temporarily stores the unipolar μ-law signal, a frame detector that detects the frame leading part of the unipolar μ-law signal and generates an address reset pulse synchronized with the frame leading position for writing to the frame buffer, a frame position comparator that measures the time lag in a position of a reference frame pulse and the address reset pulse for writing to the frame buffer and generates an address reset pulse for reading from the frame buffer, and a serial-parallel converter that converts and outputs a serial μ-law PCM signal read from the frame buffer to parallel μ-law PCM signals; a multiplexer that time-division multiplexes plural parallel μ-law PCM signals and outputs a time-division multiplexed μ-law PCM signal; a μ-law-to-A-law converter that converts the time-division multiplexed μ-law PCM signal to a time-division multiplexed A-law PCM signal; a demultiplexer that demultiplexes the time-division multiplexed A-law PCM signal and outputs plural parallel A-law PCM signals; and an A-law signal output circuit that receives the parallel A-law PCM signals and outputs a serial A-law PCM signal.
 2. μ-law-to-A-law translating equipment according to claim 1, comprising: respective plural and the same number of μ-law signal receiving circuits and A-law signal output circuits.
 3. μ-law-to-A-law translating equipment according to claim 1, wherein: the A-law signal output circuit comprises: a parallel-serial converter that converts parallel A-law PCM signals to a serial A-law PCM signal; and a frame inserter that inserts a frame bit into the serial A-law PCM signal.
 4. μ-law-to-A-law translating equipment according to claim 3, wherein: the frame inserter inserts a frame bit according to a reference frame pulse.
 5. μ-law-to-A-law translating equipment according to claim 3, wherein: the A-law signal output circuit further comprises: a line driver that outputs a serial A-law PCM signal at a predetermined output amplitude level.
 6. A-law-to-μ-law translating equipment, comprising: a timing pulse generator that generates a reference frame pulse; an A-law signal receiving circuit that receives an A-law PCM signal and outputs parallel A-law PCM signals according to a reference frame pulse, said A-law receiving circuit comprises: a line receiver that converts an A-law PCM signal from bipolar to unipolar and outputs a unipolar A-law signal, a frame buffer that temporarily stores the unipolar A-law signal, a frame detector that detects the frame leading part of the unipolar A-law signal and generates an address reset pulse synchronized with the frame leading position for writing to the frame buffer, a frame position comparator that measures the time lag in a position of a reference frame pulse and the address reset pulse for writing to the frame buffer and generates an address reset pulse for reading from the frame buffer, and a serial-parallel converter that converts a serial A-law PCM signal read from the frame buffer to parallel A-law PCM signals; a multiplexer that time-division multiplexes plural parallel A-law PCM signals and outputs a time-division multiplexed A-law PCM signal; an A-law-to-μ-law converter that converts the time-division multiplexed A-law PCM signal to a time-division multiplexed μ-law PCM signal; a demultiplexer that demultiplexes the time-division multiplexed μ-law PCM signal and outputs plural parallel μ-law PCM signals; and a μ-law signal output circuit that receives parallel μ-law PCM signals and outputs a serial μ-law PCM signal.
 7. A-law-to-μ-law translating equipment according to claim 6, comprising: respective plural and the same number of A-law signal receiving circuits and μ-law signal output circuits.
 8. A-law-to-μ-law translating equipment according to claim 6, wherein: the μ-law signal output circuit comprises: a parallel-serial converter that converts parallel μ-law PCM signals to a serial μ-law PCM signal; and a frame inserter that inserts a frame bit into the serial μ-law PCM signal.
 9. A-law-to-μ-law translating equipment according to claim 8, wherein: the frame inserter adds a frame bit to the serial μ-law PCM signal according to a reference frame pulse.
 10. A-law-to-μ-law translating equipment according to claim 8, wherein: the μ-law signal output circuit further comprises: a line driver that outputs a serial μ-law PCM signal at a predetermined output amplitude level. 